1. Field of the Invention
The present invention is related to cable modem systems. In particular, the present invention is related to a cable modem system and method for data transfer.
2. Background
Conventional cable modem systems utilize DOCSIS-compliant equipment and protocols to transfer data between one or more cable modems (CM) and a cable modem termination system (CMTS). DOCSIS (Data Over Cable System Interface Specification) generally refers to a group of specifications that define industry standards for cable headend and cable modem equipment. In part, DOCSIS sets forth requirements and objectives for various aspects of cable modem systems including operations support systems, management, data interfaces, as well as network layer, data link layer, and physical layer transport for cable modem systems.
At a high level, DOCSIS comprises a four-way handshake protocol with the following message exchange: (1) request for bandwidth for data transmission by a cable modem, (2) grant of request by the CMTS, (3) upstream slot specification by the CMTS, and (4) subsequent data transmission by the cable modem. Both slot specification and grant messages are encapsulated in a single DOCSIS message known as the MAP, which in fact includes all feedback from the CMTS to cable modems related to the normal mode of operation of the DOCSIS protocol.
After the grant from the CMTS has been received by the cable modem, the upstream channel may be viewed as a continuous flow of mini-slots that may be used to transmit data in ways that depart from, and are more efficient than, standard DOCSIS protocols. For example, voice and data packets may be processed by the cable modem to reduce the number of bits transferred per packet through the elimination of protocol overhead. In particular, a proprietary protocol-specific header compression technique may be used to reduce the size of various protocol headers within a given DOCSIS packet. The use of a protocol-specific header compression technique presents a distinct advantage over DOCSIS 1.0, which does not provide for header suppression, as well as over DOCSIS 1.1, which only permits header suppression based on the presence of redundant bit sequences in sequentially-transmitted packets.
Techniques that reduce the number of bits transferred per packet as described above require additional processing by the CMTS to reconstruct the original DOCSIS packet and the protocol headers included therein so that the packet may be properly handled at the cable headend. However, conventional CMTS equipment does not provide for such additional processing capabilities. Moreover, the cost of replacing or upgrading existing CMTS equipment to provide for these capabilities may be prohibitively expensive. Accordingly, what is desired is a cable modem system and method for data transfer that provides for specialized headend processing of modified DOCSIS packets while utilizing existing conventional CMTS equipment with little or no modification.